Wireless communication systems have grown in popularity as they have become more accessible, affordable, and reliable. In researching methods to improve the reliability and voice quality of wireless devices, such as cellular telephones, designers have sought new ways to efficiently communicate with a wireless device as it moves.
While numerous system architectures are available, the components of a wireless system typically include a mobile radio device (i.e., cell phone), a radio base station, a switch or network control device, and a backbone network to which the wireless communication system provides access.
Today, the most common mobile wireless networks are the cellular telephone networks. Cellular networks are designed using various modulation techniques for transmitting information. Most mobile wireless companies are turning to digital communication over analog communication techniques for multiple access because digital communication techniques are able to improve performance as well as support many more users in a given frequency spectrum. Common multiple access techniques that are based on digital modulation include frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA), and global system for mobile communication (GSM). The mobile wireless industry had undergone multiple generations from the first generation (analog/digital cellular telephony) to the second generation (digital personal communication services, or PCS) to the third generation (digital multimedia services, soon to be launched). The third generation partnership project (3GPP) is one of the third generation wireless standards based on CDMA technology and will deployed worldwide (see, http://www.3gpp.org and ftp://ftp.3gpp.org).
Typical wireless cellular systems utilize fixed base transceivers (i.e., base station) to support certain geographic areas. The geographic areas are divided into small areas, referred to as cell sites. Coverage provided by a certain base station is measured as a radius from the base station antenna. Each cell site may be supported by a single base station or wherein the cell site may be subdivided into smaller sub-cells through cell splitting and/or sectorization by steering antenna patterns.
In a typical operating environment, a wireless device user moves from cell to cell while operating the wireless device. Such movement creates challenges for the wireless network designer. The wireless network must be able to efficiently pass an active transmission from one base station to another as the user moves between cells. The process is referred to as a handoff.
Typically, a handoff is performed when the base station currently communicating with the mobile device detects that the received signal strength from the mobile device has dropped below a predetermined level. This low signal strength indicates that the user may be approaching a cell boundary. When this occurs, the cellular system determines whether another base station or another sector within the same base station is receiving a stronger signal from the mobile device.
There are two basic types of handoffs that a wireless system may employ. The first type of handoff is the hard handoff. Hard handoffs are characterized by the break-before-make strategy. Hard handoffs discontinue communication with the current base station prior to connecting to the new base station. The second basic type of handoff is the soft handoff. Soft handoffs are characterized by a make-before-break strategy. Accordingly, the mobile device communicates on multiple radio links with one or more base stations simultaneously during the call while performing soft handoff. Soft handoff is a unique handoff method that characterizes CDMA technology.
Within the category of soft handoffs, are softer handoffs. Softer handoffs are used when two or more out of all the radio links in a call are established on sectors of the same cell site. The introduction of second and third generation CDMA systems has imposed a large demand on the number of radio links per call for performance purposes (e.g., up to 6 links for 3GPP). Furthermore, the capacity requirements in metropolitan areas have imposed a large demand on sectorization (up to 6 sectors per cell site). Therefore, it is likely in many scenarios that many (e.g., 4 out of 6) sectors can be involved in softer handoffs.
To perform soft or softer handoffs, a mobile device must be able to communicate on multiple radio links with multiple base stations simultaneously during the call. This is generally accomplished by utilizing multiple transceivers within a single wireless user device. When designing transceiver boards in the base station, it is necessary to assign signal buffers which store the data to be transmitted (or received) to multiple processors, e.g., transmitters (or receivers). For example, in a CDMA system, a “softer” handoff requirement implies that multiple copies of the call signal may be transmitted over multiple sectors of the same base station. Hence, data is to be downloaded from a buffer (e.g., memory device) onto several transmitter devices—in the base station—such that multiple copies of the data may be transmitted. Thus, a base station assigns a single data server (e.g., buffer) to the call, with multiple processors (transmitters/receivers) to support all links on all sectors for such call. In the presence of many calls, that have been setup with the same base station, it is imperative to design an efficient scheme/architecture that would organize the communication between signal buffers (e.g., data servers) and the available transmitter/receiver devices (e.g., processors). Current solutions to the problem include fixed assignment schemes and pooled assignment schemes.
Therefore, it is evident that there is a need in the art for systems and methods for providing a processor assignment scheme that efficiently assigns processors to data servers. Additionally, it is evident that there is a need in the art for systems and methods for providing a processor assignment scheme with a manageably sized shared medium.